Field of the Invention
The present invention relates generally to electronic circuitry. More specifically, the present invention relates to a method for manufacturing a surface mount device (SMD).
Introduction to the Invention
Surface mount devices (SMDs) are utilized in electronic circuits because of their small size. Generally, SMDs comprise a core device embedded within a housing material, such as plastic or epoxy. For example, a core device with resistive properties may be embedded in the housing material to produce a surface mount resistor.
One disadvantage with existing SMDs is that the materials utilized to encapsulate the core device tend to allow oxygen to permeate into the core device itself. This could be adverse for certain core devices. For example, the resistance of a positive-temperature-coefficient core device tends to increase over time if oxygen is allowed to enter the core device. In some cases, the base resistance may increase by a factor of five (5), which may take the core device out of spec.
To overcome these problems, the core device may be encapsulated with a low oxygen permeability, such as the oxygen barrier material described in U.S. Pat. No. 8,525,635, issued Sep. 3, 2013 (Navarro et al.), and U.S. Publication No. 2011/0011533, published Jan. 20, 2011 (Golden et al.).
Current methods for manufacturing SMDs such as those described above yield SMDs with a relatively large volume of encapsulant in comparison to the total volume of the SMD. For example, the volume of the encapsulant may correspond to 35-40% of the total volume.